Known display devices are active matrix display devices in which a plurality of pixels arranged in matrix include the respective switches. Each pixel displays an image in accordance with a desired potential (image signal) input through the switch.
Active matrix display devices require a circuit (scan line driver circuit) that controls switching of the switches provided in the pixels by controlling potentials of scan lines. A general scan line driver circuit includes an n-channel transistor and a p-channel transistor in combination, but a scan line driver circuit can also be formed using either n-channel transistors or p-channel transistors. Note that the former scan line driver circuit can have lower power consumption than the latter scan line driver circuit. On the other hand, the latter scan line driver circuit can be formed through a smaller number of manufacturing steps than the former scan line driver circuit.
When the scan line driver circuit is formed using either n-channel transistors or p-channel transistors, a potential output to a scan line changes from a power supply potential output to the scan line driver circuit. Specifically, when the scan line driver circuit is formed using only n-channel transistors, at least one n-channel transistor is provided between the scan line and a wiring for supplying a high power supply potential to the scan line driver circuit. Accordingly, a high potential that can be output to the scan line is decreased from the high power supply potential by the threshold voltage of the at least one n-channel transistor. In a similar manner, when the scan line driver circuit is formed using only p-channel transistors, a low potential that can be output to the scan line is increased from a low power supply potential supplied to the scan line driver circuit.
In response to the above problem, it has been proposed to provide a scan line driver circuit which is formed using either n-channel transistors or p-channel transistors and which can output, to a scan line, a power supply potential supplied to the scan line driver circuit, without a change.
For example, a scan line driver circuit disclosed in Patent Document 1 includes an n-channel transistor that controls electrical connection between scan lines and clock signals alternating between a high power supply potential and a low power supply potential at a constant frequency. When the high power supply potential is input to a drain of the n-channel transistor, a potential of a gate thereof can be increased by using capacitive coupling between the gate and a source thereof. Thus, in the scan line driver circuit disclosed in Patent Document 1, the same or substantially the same potential as the high power supply potential can be output from the source of the n-channel transistor to the scan lines.
The number of the switches provided in each pixel arranged in the active matrix display device is not limited to one. Some display devices include a plurality of switches in each pixel and control the respective switching separately to display an image. For example, Patent Document 2 discloses a display device including two kinds of transistors (p-channel transistor and n-channel transistor) in each pixel and the switching of the transistors are controlled separately by different scan lines. In order to control potentials of the separately provided two kinds of scan lines, two kinds of scan line driver circuits (scan line driver circuit A and scan line driver circuit B) are further provided. In the display device disclosed in Patent Document 2, the separately provided scan line driver circuits output, to the scan lines, signals having substantially opposite phases.